Everything you need to know before hiring a extension builder in the UK — from costs and qualifications to what to expect and how to handle problems.
What does an extension builder do, and what does it cost in the UK?
An extension builder handles groundwork, structure, roof and finishing for a single- or double-storey home extension. UK 2026 typical cost: £1,500–£2,500 per m² (London: +30–40%). A 4×5m single-storey rear runs £30,000–£60,000. Most need Building Regs approval; some need full planning permission. Allow 10–14 weeks for single, 14–20 for double.
The average cost for a extension builder in the UK is £15,000–£50,000, though prices vary by location, job complexity and materials. London and South East prices are typically 20–40% higher than the national average. Always get at least 3 quotes to compare — TradeMatch makes this free and easy.
For well-defined jobs, a fixed quote protects you from unexpected costs. Day rates (typically £150–£300) suit exploratory or ongoing work where the scope may change. Ask your extension builder to break down the quote into labour, materials and VAT so you can compare fairly.
Most reputable extension builders offer free, no-obligation quotes for standard work. Some may charge for detailed surveys or assessments on larger projects — this should be agreed upfront. On TradeMatch, all initial quotes are free.
Look for these credentials: Relevant trade qualifications, Public liability insurance. Accreditation from Relevant trade association confirms they meet industry standards. On TradeMatch, every extension builder is background-checked and their qualifications are verified before they can accept work.
Yes — always check for public liability insurance (minimum £1 million) and, for employees, employers' liability insurance. This protects you if something goes wrong. Professional indemnity insurance is also valuable for design or advisory work. Never hire uninsured tradespeople.
Verify their credentials with Relevant trade association, check online reviews from multiple sources, ask for references from recent jobs, confirm their insurance is current, and check they have a registered business address. TradeMatch verifies all of this before a tradesperson can join the platform.
Get at least 3 quotes to compare pricing, approach and timeline. This gives you a fair picture of market rates and helps identify outliers — both suspiciously cheap and overpriced. TradeMatch sends your job to up to 5 vetted professionals automatically.
A good quote should include: an itemised breakdown of labour and materials, the total cost including VAT, a clear timeline with start and completion dates, payment schedule and terms, and any exclusions or assumptions. Be wary of vague or verbal-only quotes.
Never pay the full amount upfront. A deposit of 10–25% is reasonable for larger jobs to cover initial materials. Stage payments linked to milestones are standard for bigger projects. TradeMatch uses escrow-protected payments — your money is held securely until you confirm the work is complete.
Small repairs and maintenance typically take 1–4 hours. Medium jobs like [object Object] usually take 1–3 days. Larger projects can take 1–4 weeks depending on complexity. Your extension builder should give you a clear timeline in their quote.
Most routine extension builder work doesn't require planning permission. However, structural changes, work on listed buildings, and projects that alter the external appearance may need approval. Building regulations may also apply — your extension builder should advise, but you can also check with your local council.
Clear the work area and provide easy access. If it's indoor work, move furniture and cover flooring. Ensure parking is available nearby. Have your requirements written down. If you've received a quote, have it to hand. Good preparation speeds up the job and can save you money.
First, raise the issue directly — most professionals will want to put things right. Document everything with photos. If the work doesn't meet the agreed specification, you have rights under the Consumer Rights Act 2015. TradeMatch's escrow system means you can raise a dispute before releasing payment.
Contact the tradesperson directly in writing first. If they're unresponsive, escalate to their trade body (Relevant trade association), leave honest reviews, and consider Trading Standards or Citizens Advice for serious issues. For TradeMatch bookings, our dispute resolution team can mediate on your behalf.
Reputable extension builders offer workmanship guarantees ranging from 12 months to 10 years depending on the work type. Get the guarantee in writing, check what it covers, and keep all documentation. Some work (like Gas Safe or electrical installations) comes with mandatory certification that acts as a guarantee.
A extension builder in the UK typically costs £15,000–£50,000. Prices depend on the job type, your location and materials. London costs are 20–40% higher. Get detailed extension builder cost guides or compare free quotes on TradeMatch.
Plain-English definitions of the credentials, schemes and technical terms most often raised when hiring a UK extension builder.
A planning right that lets you extend without full planning permission inside set limits (e.g. 4m rear depth on a semi). Conservation areas and Article 4 Directions remove or restrict it.
The technical standards for structure, insulation, fire safety and ventilation. All extensions need Building Control sign-off, even when planning permission is not required.
The law governing work to walls shared with a neighbour. You must serve notice 1–2 months before excavating within 3m of a boundary or cutting into a party wall.
Standard Assessment Procedure — the energy calculation submitted with most extension applications. Required to demonstrate Part L1A compliance.
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